Apparatus for detecting temperature of semiconductor elements for power conversion

ABSTRACT

An apparatus for detecting temperatures of power-conversion semiconductor elements, which is applicable to a system including a plurality of power-conversion semiconductor elements and a plurality of temperature signal outputs for outputting temperature signals correlated to temperatures of the respective semiconductor elements. In the apparatus, the temperature signal outputted from at least one of the temperature signal outputs is input directly to a microcomputer without passing through at least one input-output interface. The temperature signals outputted from the other two or more temperature signal outputs are input to a plurality of input ports of the at least one input-output interface sequentially connected to an output of the interface. The microcomputer detects the temperatures of the respective semiconductor elements based on the temperature signals received from the output port of the at least one input-output interface and the temperature signal received directly from the at least one of the temperature signal outputs.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority fromearlier Japanese Patent Applications No. 2013-255769 field Dec. 11, 2013and No. 2014-220603 filed Oct. 29, 2014, the descriptions of which areincorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to an apparatus for detecting temperaturesof semiconductor elements for power conversion.

2. Related Art

Conventionally, a known power converter, as disclosed in Japanese PatentApplication Laid-Open Publication No. 2008-206345, includes a pluralityof switching elements, such as insulated gate bipolar transistors(IGBTs), is configured such that temperatures of some of the pluralityof switching elements can be detected by temperature sensing elements.More specifically, in such a power converter, a prespecified one of theswitching elements is assumed to be hottest among the switching elementsduring use. In such a power converter, the plurality of switchingelements are de-energized, when the detected temperature of theprespecified switching element has reached a predetermined thresholdtemperature. Such a power converter is thus intended to protect theswitching elements from overheating.

Such a configuration that temperatures of some of the plurality ofswitching elements are detected may give rise to the followingdisadvantages.

Even though the prespecified one of the switching elements is assumed atthe time of designing to be hottest during use, another switchingelement may actually be hottest among the switching elements during usedue to aging or the like of the power converter. There is a disadvantagethat, if the power converter is not configured to detect a temperatureof such another switching element, all the switching elements couldn'tbe reliably protected from overheating based on the detected temperatureof the prespecified one of the switching elements assumed at the time ofdesigning to be hottest during use.

In addition, the temperatures of the respective switching elements mayvary during flowing of collector currents through the respectiveswitching elements due to their aging or individual difference.Therefore, when the power converter is configured to detect temperaturesof some of the switching elements, the threshold temperature that isused to protect the switching elements from overheating needs to be setlower than an upper limit by a large margin for safety, below whichupper limit the reliability of the switching elements can be retained.However, in such a configuration, there is a disadvantage that theoverheat protecting process may be performed even though the actualtemperatures of the switching elements have not yet reached theupper-limit temperature, and a temperature range where use of theswitching elements is restricted may enlarge.

Power-conversion semiconductor elements, whether switching elements ornot, may suffer from such disadvantages.

In consideration of the foregoing, exemplary embodiments of the presentinvention are directed to providing an apparatus for detectingtemperatures of a plurality of semiconductor elements for powerconversion, capable of preventing the semiconductor elements fromoverheating and preventing enlargement of a temperature range where useis restricted.

SUMMARY

In accordance with an exemplary embodiment of the present invention,there is provided an apparatus for detecting temperatures ofpower-conversion semiconductor elements, the apparatus being applicableto a system including a plurality of power-conversion semiconductorelements that produce heat when energized, a plurality of temperaturesignal outputs associated with the respective power-conversionsemiconductor elements, the temperature signal outputs being configuredto output temperature signals correlated to temperatures of therespective power-conversion semiconductor elements, the apparatusincluding: a microcomputer configured to detect the temperatures of therespective power-conversion semiconductor elements based on thetemperature signals outputted from the respective temperature signaloutputs, at least one input-output interface having a plurality of inputports and an output port selectively connected to one of the pluralityof input ports, wherein the temperature signal outputted from at leastone of the plurality of temperature signal outputs is input directly tothe microcomputer without passing through the at least one input-outputinterface, and the temperature signals outputted from the other two ormore temperature signal outputs are input to the respective input portsof the at least one input-output interface, the microcomputer isconfigured to detect the temperatures of the respective power-conversionsemiconductor elements based on the temperature signals received fromthe output port of the at least one input-output interface and thetemperature signal received directly from the at least one of theplurality of temperature signal outputs.

In the above embodiment, the temperature signal outputs are provided forthe respective power-conversion semiconductor elements. This allows themicrocomputer to detect the temperature of each of the plurality ofpower-conversion semiconductor elements. Hence, even though aprespecified one of the switching elements is initially assumed to behottest during use of the system, another switching element may actuallybe hottest among the switching elements during use due to aging or thelike of the system. Even in such a case, the microcomputer is able todetermine which semiconductor element is hottest among the plurality ofswitching elements. It is thus possible to prevent the semiconductorelements from overheating and prevent enlargement of a temperature rangewhere use of the system is restricted.

In addition, in the above embodiment, the temperature signal outputtedfrom at least one of the plurality of temperature signal outputs isinput directly to the microcomputer without passing through the at leastone input-output interface. Therefore, even if the at least oneinput-output interface fails, paths can be ensured between themicrocomputer and the temperature signal outputs other than the at leastone of the temperature signal outputs that is not connected to the atleast one input-output interface. Even if the at least one input-outputinterface fails, this can achieve fail-safe, such as power saving, andcan thus prevent substantial degradation of the reliability of thesystem.

In addition, in the above embodiment, signal transferring paths betweenthe microcomputer and the other two or more temperature signal outputscan be established by using the input-output interface. The input-outputinterface is configured such that the number of output ports is lessthan the number of input ports. Therefore, the number of input ports ofthe microcomputer required to detect the temperatures of the respectivepower-conversion semiconductor elements can be reduced less than thetotal number of power-conversion semiconductor elements. This allows theapparatus to be downsized and costs of the apparatus to be reduced.

In another embodiment, the apparatus is applied to a system including aplurality of power-conversion semiconductor elements that produce heatwhen energized, and a plurality of temperature signal outputs associatedwith the respective power-conversion semiconductor elements, where thetemperature signal outputs are configured to output temperature signalscorrelated to temperatures of the respective power-conversionsemiconductor elements. The apparatus includes a microcomputer having aplurality of input ports for receiving the temperature signals from therespective temperature signal outputs, each for a respective one of thetemperature signals, and is configured to detect the temperatures of therespective power-conversion semiconductor elements based on thetemperature signals received at the respective input ports.

In the above other embodiment, the temperature signal outputs areprovided for the plurality of power-conversion semiconductor elements,one for each power-conversion semiconductor element. The microcomputerhas the plurality of input ports for respectively receiving thetemperature signals from the respective temperature signal outputs. Thatis, in the microcomputer is configured such that the number of thetemperature signal outputs is equal to the number of the input ports.Thus, the microcomputer is able to detect the temperatures of therespective whole power-conversion semiconductor elements. Even though aprespecified one of the switching elements is initially assumed to behottest during use of the system, another switching element may actuallybe hottest among the switching elements during use due to aging or thelike of the system. Even in such a case, the microcomputer is able todetermine which semiconductor element is hottest among the plurality ofswitching elements. It is thus possible to prevent the semiconductorelements from overheating and prevent enlargement of a temperature rangewhere use of the system is restricted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a three-phase inverter in accordancewith a first embodiment of the present invention;

FIG. 2 is a cross-sectional view of the three-phase inverter taken alongline 2-2 of FIG. 1;

FIG. 3 is a schematic diagram of a motor control system in accordancewith the first embodiment;

FIG. 4 is a schematic circuit diagram for transferring temperaturesignals in accordance with the first embodiment;

FIG. 5 is a schematic of temperature estimation errors for IGBTs;

FIG. 6 is a schematic circuit diagram for transferring temperaturesignals in accordance with a second embodiment of the present invention;

FIG. 7 is a schematic diagram of a motor control system in accordancewith a third embodiment of the present invention;

FIG. 8 is a schematic circuit diagram for transferring temperaturesignals in accordance with the third embodiment;

FIG. 9 is a schematic circuit diagram for transferring temperaturesignals in accordance with a fourth embodiment of the present invention;

FIG. 10 is a schematic circuit diagram for transferring temperaturesignals in accordance with a fifth embodiment of the present invention;

FIG. 11 is a schematic diagram of a buck-boost converter in accordancewith a sixth embodiment of the present invention;

FIG. 12 is a schematic diagram of a motor control system in accordancewith a seventh embodiment of the present invention;

FIG. 13 is a schematic circuit diagram for transferring temperaturesignals in accordance with an eighth embodiment; and

FIG. 14 is an example of time-multiplexed frame signal in accordancewith the eighth embodiment.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Embodiments of the present invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout.

First Embodiment

There will now be explained a temperature detection apparatus applied toa vehicle-mounted power converter (a three-phase inverter) in accordancewith a first embodiment of the present invention with reference to theaccompanying drawings.

The three-phase inverter of the first embodiment will be explained withreference to FIGS. 1 and 2.

As shown in FIGS. 1 and 2, the three-phase inverter 10 includes acircuit board 20, a cooler 30, a frame 40, U-, V-, W-phase upper-armsemiconductor modules 50Up, 50Vp, 50Wp, and U-, V-, W-phase lower-armsemiconductor modules 50Un, 50Vn, 50Wn.

Each semiconductor module 50αβ (α=U, V, W: β=p, n) is a member, intowhich a switching element, a freewheel diode electrically connected inanti-parallel with the switching element, and a temperature-sensitivediode for detecting a temperature of the switching element aremodularized. In the present embodiment, an insulated gate bipolartransistors (IGBT) is used as the switching element. The switchingelement and the temperature-sensitive diode are formed on the same chip.

Each semiconductor module 50αβ has a body including therein theswitching element, the freewheel diode, and the temperature-sensitivediode. The body is a flattened cuboid. A plurality of control terminalsprotrude from and perpendicularly to one of surfaces of the body. Theplurality of control terminals include a gate terminal and an emitterterminal (referred to as a Kelvin emitter terminal) of the switchingelement.

Each semiconductor module 50αβ is secured to the circuit board 20 viathe control terminals. More specifically, each semiconductor module 50αβis secured to the circuit board 20 by soldering the control terminals tothe circuit board 20.

The frame 40 surrounds the six semiconductor modules 50αβ. The circuitboard 20 is secured on top of the frame 40. For example, the frame 40 isstiff enough to compressively hold the cooler 30 and the respectivesemiconductor modules 50αβ, and made of a material capable of blockingswitching noise (e.g., metal or conductive resin).

The circuit board 20 is rectangular in shape as viewed from aperpendicular direction to a front surface of the circuit board 20. Thecircuit board 20 is functional to turn on and off the switching elementsof the respective semiconductor modules 50αβ. This function of thecircuit board 20 is realized by an electronic component, such as amicrocomputer or the like, mounted on the circuit board 20.

The cooler 30 includes an inlet line 30 a, an outlet line 30 b, and aplurality of (e.g., four) cooling members 30 c, and is secured to theframe 40. The inlet line 30 a is a member for introducing a coolingfluid for cooling the respective semiconductor modules 50αβinto thethree-phase inverter 10. The outlet line 30 b is a member for outputtingthe cooling fluid from the three-phase inverter 10. Each of the coolingmembers 30 c connects the inlet line 30 a and the outlet line 30 b todirect the cooling fluid from the inlet line 30 a to the outlet line 30b.

The cooling members 30 c are each a flattened cuboid in shape andarranged in line. For each pair of upper-arm semiconductor module 50αpand lower-arm semiconductor module 50αn (α=U, V, W), the upper-armsemiconductor module 50αp and the lower-arm semiconductor module 50αn ofthe same phase are arranged in line between a pair of adjacent coolingmembers 30 c. More specifically, the semiconductor modules 50αp, 50αn ofthe same phase are arranged in line along the longitudinal direction ofthe cooling members 30 c (a direction from the inlet line 30 a to theoutlet line). The upper-arm semiconductor module 50αp is arrangedupstream of the lower-arm semiconductor module 50αn along a flow path ofthe cooling fluid including the inlet line 30 a, the outlet line 30 b,and the cooling members 30 c. The pairs of upper-arm semiconductormodule 50αp and lower-arm semiconductor module 50αn (α=U, V, W) and theplurality of cooling members 30 c are stacked alternately, therebyforming a stack.

A wall member 42 is provided on an inner circumferential wall of theframe 40. On a side of the wall member 42 facing the stack is formed awall surface. In the present embodiment, the wall member 42 is made ofthe same material as the frame 40.

A pressing member 60 is provided on a portion of the innercircumferential wall of the frame 40 facing the wall member 42 withmounting pins 62 between the pressing member 60 and the portion of theinner circumferential wall. The pressing member 60 is a member forpushing the stack of the cooling members 30 c and the semiconductormodules 50αβ toward the wall member 42. More specifically, one ofopposite sides of the stack is pushed by the pressing member 60 towardthe wall member 42 with the other of opposite sides of the stack (a sideof the leftmost cooling member 30 c facing the wall member 42) kept incontact with the wall surface of the wall member 42. This can enhancethe fit between the cooling members 30 c and their respective adjacentsemiconductor modules, thereby enhancing the heat dissipation of thesemiconductor modules. In the present embodiment, a plate spring is usedas the pressing member 60. In the present embodiment, the stack ispushed by the pressing member 60 via the plate member 64. An arc-likeportion of the pressing member 60 is pressed directly onto the platemember 64, thus indirectly onto the stack, which can prevent the coolingmembers 30 c from being considerably deformed.

In the cooler 30 configured as above, when the cooling fluid isintroduced form the inlet line 30 a, the cooling fluid flows through therespective cooling members 30 c. The cooling fluid is output from theoutlet line 30 b after flowing through the respective cooling members 30c, thereby cooling the respective semiconductor modules 50αβ.

In the present embodiment, it is assumed that there is the hottest oneof the six semiconductor modules 50αβ (α=U, V, W: β=p, n) during use(that is, while the switching elements Sαβ of the three-phase inverter10 are turned on and off). In the present embodiment, it is assumed thatthe hottest one of the six semiconductor modules is the V-phaselower-arm semiconductor module 50Vn that is on the downstream side ofthe cooling fluid and between the middle pair of the adjacent coolingmembers 30 c. In addition, it is further assumed that the second hottestone of the six semiconductor modules is the W-phase lower-armsemiconductor module 50Wp.

That is, during use of the three-phase inverter 10, a temperature of thecooling fluid on the downstream side of the flow path of the coolingfluid is greater than a temperature of the cooling fluid on the upstreamside of the flow path of the cooling fluid. Therefore, during use of thethree-phase inverter 10, a temperature of the semiconductor module 50αnon the downstream side of the flow path is greater than a temperature ofthe semiconductor module 50αp on the upstream side of the flow path.Each cooling member 30 c other than the cooling members 30 c adjacentthe V-phase semiconductor modules 50Vβ (50Vp, 50Vn) are in contact witheither the wall member 42 or the plate member 64. Therefore, an amountof heat dissipated from each cooling member 30 c (along the heatdissipation path) other than the cooling members 30 c adjacent theV-phase semiconductor modules 50Vβ is greater than an amount of heatdissipated from each cooling member 30 c (along the heat dissipationpath) adjacent the V-phase semiconductor modules 50Vβ. Therefore, thecenter V-phase semiconductor modules 50Vβ are prone to be hotter.Besides this reason, since collector currents of the switching elementsof the respective semiconductor module 50αβ have the substantially sameaverage value, the V-phase lower-arm semiconductor module 50Vn ishottest, and the W-phase lower-arm semiconductor module 50Wp is secondhottest.

An overall configuration of a motor control system of the presentembodiment will now be explained with reference to FIG. 3.

As shown in FIG. 3, the motor control system includes the three-phaseinverter 10 and a motor generator 70. The motor generator 70 isconnected to a driven wheel (not shown) and acts as a vehicle primemover or the like. In the present embodiment, a one-motor control systemincluding one motor generator 70 is used as the motor control system. Apermanent magnet synchronous electrical motor may be used as the motorgenerator 70.

The three-phase inverter 10 is electrically connected to a high-voltagebattery 72, such as a lithium-ion secondary battery, anickel-metal-hydride secondary battery or the like, as a direct-current(DC) power source.

Collector terminals of the U-, V-, W-phase upper-arm switching elementsSUp, SVp, SWp of the respective U-, V-, W-phase upper-arm semiconductormodules 50Up, 50Vp 50Wp are electrically connected to each other.Emitter terminals of the U-, V-, W-phase lower-arm switching elementsSUn, SVn, SWn of the respective U-, V-, W-phase lower-arm semiconductormodules 50Un, 50Vn, 50Wn are electrically connected to each other. Thecollector terminals are electrically connected to a positive terminal ofthe high-voltage battery 72. The emitter terminals are electricallyconnected to a negative terminal of the high-voltage battery 72.

An emitter terminal of the α-phase upper-arm switching element Sαp (α=U,V, W) is electrically connected to a collector terminal of the α-phaselower-arm switching element Sαn. A junction between the emitter terminalof the α-phase upper-arm switching element Sαp and the collectorterminal of the α-phase lower-arm switching element Sαn is electricallyconnected to an α-phase terminal of the motor generator 70.

The three-phase inverter 10 includes a microcomputer 80 and drivecircuits Drαβ (α=U, V, W: β=p, n). The microcomputer 80 includes acentral processing unit (CPU) and others to generate operation signalsgαβ and output the operation signals gαβ to the respective drivecircuits Drαβ, thereby controlling a controlled variable (e.g., torque)of the motor generator 70 to a command value. Each drive circuit Drαβ isa gate drive circuit for charging and discharging a gate of theswitching element Sαβ in response to the operation signal gαβ. Theswitching element Sαβ is turned on and off by the drive circuit Drαβ.The operation signals gαβ are signals for passing sinusoidal currentsthat are 120 degrees out of phase. For example, the operation signalsgαβ may be generated in the well-known field-oriented control loop.

In the present embodiment, the vehicle includes a high-voltage domainand a low-voltage domain. The high-voltage domain includes the motorgenerator 70, the high-voltage battery 72, the semiconductor modules50αβ and the drive circuits Drαβ (α=U, V, W: β=p, n). The low-voltagedomain includes the microcomputer 80. A reference potential VstL of thelow-voltage domain and a reference potential VstH of the high-voltagedomain are different from each other. In the present embodiment, thereference potential VstH of the high-voltage domain is set to anegative-electrode potential of the high-voltage battery 72, and thereference potential VstL of the low-voltage domain is set to a potentialof the vehicle body that is a median of the positive-electrode andnegative-electrode potentials of the high-voltage battery 72.

Temperature detection for the respective switching elements Sαβ (α=U, V,W: β=p, n) will now be explained with reference to FIG. 4. FIG. 4 showsvarious electronic components mounted on the respective semiconductormodules 50αβ and the circuit board 20.

As shown in FIG. 4, the drive circuits Drαβ (α=U, V, W: β=p, n),photocouplers Cαβ (α=U, V, W: β=p, n), first and second multiplexers 82a, 82 b, and the microcomputer 80 are mounted on the circuit board 20.Each of the first and second multiplexers 82 a, 82 b has two input ports(first input port Tin1, second input port Tin2), and one output portTout. In the present embodiment, each of the first and secondmultiplexers 82 a, 82 b corresponds to an input-output interface.

The drive circuits Drαβ are configured to receive temperature signalsfrom the respective temperature-sensitive diodes Tαβ. In the presentembodiment, the temperature-sensitive diodes Tαβ are supplied withcurrent from a constant current source (not shown). Therefore, thetemperature-sensitive diodes Tαβ are configured to output voltagesignals negatively correlated to temperatures of the respectiveswitching elements Sαβ. In the present embodiment, eachtemperature-sensitive diode Tαβ corresponds to a temperature signaloutput.

The drive circuits Drαβ are configured to receive the temperaturesignals from the respective temperature-sensitive diodes Tαβ. The drivecircuit Drαβ are configured to output the received temperature signalsto the respective photocouplers Cαβ. In the present embodiment, eachdrive circuit Drαβ is configured to, based on comparison of the receivedtemperature signal from the temperature-sensitive diode Tαβ with acarrier signal (e.g., a triangular waveform signal) in magnitude,convert the temperature signal into a duty ratio signal (referred to asa duty signal) and output the duty ratio signal to the photocoupler Cαβ.

Each photocoupler Cαβ is an optical insulating transfer elementconfigured to transmit a signal from the high voltage domain to the lowvoltage domain while electrically isolating the high and low voltagedomains from each other. At an input (photodiode-side) of thephotocoupler Cαβ is received the temperature signal (i.e., the dutyratio signal) of the temperature-sensitive diode Tαβ from the drivecircuit Drαβ.

From an output (phototransistor-side) of each of the U-, V-phaseupper-arm photocouplers CUp, CVp, the temperature signal is input to themicrocomputer 80 via the first multiplexer 82i a. More specifically, theoutput of the U-phase upper-arm photocoupler CUp is connected directlyto the first input port Tin1 of the first multiplexer 82 a via a firstinput channel Lin1. The output of the V-phase upper-arm photocoupler CVpis connected directly to the second input port Tin2 of the firstmultiplexer 82 a via a second input channel Lin2. In the presentembodiment, the input channels Lin1, Lin2 use a wiring pattern formed onthe circuit board 20.

An output port Tout of the first multiplexer 82 a is connected directlyto a first input port T1 of the microcomputer 80 via an output channelLout. In the present embodiment, the output channel Lout uses the wiringpattern formed on the circuit board 20. The first multiplexer 82 a isconfigured to sequentially select one of the first and second inputports Tin1, Tin2 to be connected to the output port Tout atpredetermined time intervals based on a switching signal (e.g., a bitsignal) received from the microcomputer 80. This allows the temperaturesignal received at the output port Tout to be alternately switchedbetween the temperature signal received at the first input port Tin1 andthe temperature signal received at the second input port Tin2 at thepredetermined time intervals.

From an output (phototransistor-side) of each of the W-phase upper-armphotocoupler CWp and the U-phase lower-arm photocoupler CUn, thetemperature signal is input to a second input port T2 of themicrocomputer 80 via the second multiplexer 82 b. A transferring mannerof the temperature signal via the second multiplexer 82 b is similar tothat of the temperature signal via the first multiplexer 82 a.Therefore, a detailed description about the transferring manner of thetemperature signal via the second multiplexer 82 b will not be givenhere.

An output of the V-phase lower-arm photocoupler CVn is connecteddirectly to a third input port Tin3 of the microcomputer 80 via aV-phase lower-arm electrical path LVn. An output of the W-phaselower-arm photocoupler CWn is connected directly to a fourth input portTin4 of the microcomputer 80 via a V-phase lower-arm electrical pathLWn. In the present embodiment, the electrical paths LVn, LWn use thewiring pattern formed on the circuit board 20.

The microcomputer 80 is configured to detect temperatures of the sixswitching elements Sαβ (α=U, V, W: β=p, n) based on the temperaturesignals received at the input ports T1 through T4. The microcomputer 80is configured to perform a power saving process when determining thatthe highest one ST of the temperatures of the six switching elementsexceeds a threshold temperature Tγ. In the power saving process, themicrocomputer 80 de-energizes the switching elements Sαβ or reducespower supplied to the switching elements Sαβ, thereby the respectiveswitching elements Sαβ from overheating.

The temperature sensing configuration as described above is employed toprevent the respective switching elements Sαβ from overheating andprevent enlargement of a temperature range where use of the respectiveswitching elements Sαβ is restricted.

The V-phase lower-arm switching element SVn is a switching element thatis assumed at the time of designing to be hottest during use among thesix switching elements Sαβ. However, another switching element may behottest during use among the six switching elements Sαβ due to aging ofthe three-phase inverter 10 or the like. Therefore, in such a case, evenif the power saving process is performed based on the temperature signalof the V-phase lower-arm switching element SVn from thetemperature-sensitive diode, the overheat condition of the otherswitching elements could not be avoided reliably.

In addition, the temperatures of the switching elements Sαβ may varyduring flowing of the collector currents through the respectiveswitching elements Sαβ due to aging or individual difference of theswitching elements. Therefore, when temperatures of some of the sixswitching elements Sαβ are detected, the threshold temperature Tγ thatis used to performed the power saving process needs to be set lower thanan upper limit by a large margin for safety, below which upper limit thereliability of the switching elements Sαβ can retained. Temperaturevariations of the switching elements will now be explained withreference to FIG. 5. In FIG. 5, a “detection element” refers to aswitching element, a temperature of which is detected, and a“non-detection element” refers to a switching element, a temperature ofwhich is not detected.

FIG. 5 shows an example case that a temperature error of each of thedetection element and the non-detection element is a maximum with thesame collector current flowing through the detection element and thenon-detection element. In FIG. 5, an “element loss” refers to an averagetemperature over a plurality of mass-produced switching elements. An“element-loss variation” refers to a variation from the averagetemperature. A “thermal resistance variation” refers to a variation intemperature among the switching elements caused by a variation inthermal resistance among new semiconductor modules. A “thermalresistance degradation” refers to an amount of temperature increase ofthe switching element caused by thermal resistance variation due toaging of the semiconductor module.

For the detection element, the element-loss minus (the element-lossvariation plus the thermal resistance variation) gives a temperaturedetected by the temperature-sensitive diode. In the example of FIG. 5,although the same collector current flows though the detection elementand the non-detection element, the temperature of the non-detectionelement is greater than the temperature of the detection element. Inthis case, a temperature of the non-detection element is a sum of theelement loss, the element-loss variation, the thermal resistancevariation, and the thermal resistance degradation. A difference intemperature between the detection element and the non-detection elementgives an actual temperature variation.

For example, when the actual temperature variation is 20° C. and theupper limit of temperatures of the switching elements is 150° C., thethreshold temperature Tγ that is used to performed the power savingprocess needs to be set to 130° C. to protect the non-detection elementfrom overheating. Thus, the threshold temperature Tγ is set lower thanthe upper limit by a large margin for safety, which may cause the powersaving process to be performed even though the temperature of thenon-detection element has not reached the upper-limit temperature. Insuch a case, there is a concern that the collector current can be nomore increased even if the collector current may be further increased.That is, there is a disadvantage that a temperature range where use ofthe switching elements is restricted may enlarge.

To overcome such a problem, in the present embodiment, temperatures ofthe six switching elements Sαβ are detected.

There are some benefits associated with the present embodiment set forthabove.

(1) The temperatures of all the six switching elements Sαβ are detected.Therefore, the hottest switching element among the six switchingelements Sαβ during use can be determined by the microcomputer 80 evenif the hottest switching element among the six switching elements Sαβduring use is changed from the switching element that is assumed at thetime of designing to be hottest among the six switching elements Sαβduring use to another one of the six switching elements Sαβ. This canprevent the six switching elements Sαβ from overheating and preventenlargement of a temperature range where the maximum value of theavailable collector current is constrained, even when it is difficult todetermine the hottest switching element among the six switching elementsSαβ only from information about the positions of the respectivesemiconductor modules within the cooler.

(2) The temperature signals outputted from two of the sixtemperature-sensitive diodes Tαβ, that is, the two temperature-sensitivediodes TVn, TWn, are transferred from the outputs of the photocouplersCVn, CWn to the microcomputer 80 via the electrical paths LVn, LWnwithout passing through the multiplexers 82 a, 82 b. Each of theelectrical paths LVn, LWn directly connecting one of the outputs of thephotocouplers CVn, CWn and the microcomputer 80 can be a path fortransferring the temperature signals in the event that the multiplexers82 a, 82 b fail. Thus, in the present embodiment, even if themultiplexers 82 a, 82 b fail, fail-safe, such as power saving, can beachieved based on the temperatures of the switching elements SVn, SWn.This can avoid substantial degradation of the reliability of thethree-phase inverter 10.

Particularly, in the present embodiment, only the V-phase lower-armtemperature-sensitive diode TVn and the W-phase lower-armtemperature-sensitive diode TWn output the temperature signals that areinput directly to the microcomputer 80. The V-phase lower-arm switchingelement SVn is assumed at the time of designing to be hottest among thesix switching elements Sαβ during use. The W-phase lower-arm switchingelement SWn is assumed to be second hottest among the six switchingelements Sαβ during use. Therefore, even if another switching element isactually hottest among the six switching elements Sαβ during use due toaging of the three-phase inverter 10 or the like, the temperatures ofThe V-phase lower-arm switching element SVn and the W-phase lower-armswitching element SWn are likely to remain at higher levels than theaverage temperature over the six switching elements Sαβ. Therefore, inthe present embodiment, even if the multiplexers 82 a, 82 b fail, thepower saving can properly protect the switching elements Sαβ fromoverheating.

(3) Paths of the temperature signals from four of the sixtemperature-sensitive diodes Tαβ, that is, the temperature-sensitivediodes Tαp (α=U, V, W), TUn, to the microcomputer 80 are realized by thetwo multiplexers 82 a, 82 b. This can reduce the number of input portsof the microcomputer 80 required to detect temperatures of the sixswitching elements Sαβ to less than the total number of switchingelements Sαβ. This allows the microcomputer 80 to detect thetemperatures of all the six switching elements Sαβ even in the presenceof a limited number of input ports of the microcomputer 80, which allowsthe three-phase inverter 10 to be downsized and costs of the three-phaseinverter 10 to be reduced.

(4) The multiplexers 82 a, 82 b are used, each of which has two inputsand one output. In each of the multiplexers 82 a, 82 b, the input to beconnected to the output port Tout is alternately switched between thetwo input ports Tin1, Tin2. This causes a delay between when thetemperature signal is received at one of the two input ports and whenthe temperature signal is output from the output port Tout to themicrocomputer 80. The delay increases with an increasing number of inputports. A difference in delay between the multiplexers 82 a, 82 bincreases with an increasing difference in number of input ports betweenthe multiplexers 82 a, 82 b. Time intervals between detection oftemperatures of each of the switching elements associated with one ofthe multiplexers 82 a, 82 b having a larger number of input ports aregreater than time intervals associated with the other of themultiplexers 82 a, 82 b. Therefore, there is a concern that overheatprotection for the switching elements by the power saving may bedelayed. In the present embodiment, the multiplexers 82 a, 82 b have anequal number of input ports, which can reduce variations in timerequired for the temperature signals to be transferred from therespective temperature-sensitive diodes Tαp, TUn to the microcomputer 80via signal transferring paths passing though the respective multiplexers82 a, 82 b. This can prevent the time intervals between detection oftemperatures of each of the switching elements Sαp, SUn from increasing,thereby preventing overheat protection from being delayed.

Particularly, in the present embodiment, the number of input ports ofeach of the multiplexers 82 a, 82 b is set to two. This can minimize thetime intervals between detection of temperatures of each of theswitching elements Sαp, SUn are detected.

Second Embodiment

There will now be explained a second embodiment of the presentinvention. Only differences of the second embodiment from the firstembodiment will be explained with reference to the accompanyingdrawings.

As shown in FIG. 6, the microcomputer 80 of the present embodimentincludes first to sixth input ports t1-t6. The first to third inputports T1, T2, T3 are electrically connected directly to outputs of theU-, V-, W-phase upper-arm photocouplers CUp, CVp, CWp via U-, V-,W-phase upper-arm electrical paths LUp, LVp, LWp. Fourth to sixth inputports T4, T5, T6 of the microcomputer 80 are electrically connecteddirectly to outputs of the U-, V-, W-phase lower-arm photocouplers CUn,CVn, CWn via U-, V-, W-phase lower-arm electrical paths LUn, LVn, LWn.In the present embodiment, the α-phase upper- and lower-arm electricalpaths Lαp, Lαn (α=U, V, W) may use the wiring pattern of the circuitboard 20.

The present embodiment described above can also prevent each of the sixswitching elements Sαβ from overheating, and can also preventenlargement of a temperature range where the available flow of collectorcurrent is constrained.

Third Embodiment

There will now be explained a third embodiment of the present invention.Only differences of the third embodiment from the first embodiment willbe explained with reference to the accompanying drawings. In the presentembodiment, a two-motor control system including two motor generators(rotating electric machines) is used as a control system. Morespecifically, as shown in FIG. 7, the control system includes anbuck-boost converter 90, a first inverter 100, a first motor generator101, a second inverter 102, a second motor generator 103, and amicrocomputer 80. Each of the motor generators 101, 103 may be apermanent magnet synchronous electrical motor. Elements having similarfunctions as in the first embodiment (see FIG. 1) are assigned the samenumbers.

The buck-boost converter 90 includes an input capacitor 91, a reactor92, voltage-transformation switching elements SCpa, SCpb, SCna, SCnb,freewheel diodes DCpa, DCpb, DCna, DCnb electrically connected inanti-parallel with the respective voltage-transformation switchingelements, and a smoothing capacitor 93. In the present embodiment, aninsulated gate bipolar transistors (IGBT) is used for each of thevoltage-transformation switching elements SCpa, SCpb, SCna, SCnb.

The buck-boost converter 90 includes a plurality of (e.g., two)upper-arm switching elements and a plurality of (e.g., two) lower-armswitching elements electrically connected in parallel with the pluralityof upper-arm switching elements. More specifically, collectors of therespective upper-arm voltage-transformation switching elements SCpa,SCpb are electrically connected to each other, and emitters of therespective upper-arm voltage-transformation switching elements SCpa,SCpb are electrically connected to each other. In addition, collectorsof the respective lower-arm voltage-transformation switching elementsSCna, SCnb are electrically connected to each other, and emitters of thelower-arm voltage-transformation switching elements SCna, SCnb areelectrically connected to each other. A series connection of theupper-arm voltage-transformation switching elements SCpa, SCpb and thelower-arm voltage-transformation switching elements SCna, SCnb iselectrically connected in parallel with the smoothing capacitor 93. Asin the first embodiment, the voltage-transformation switching elementsSCpa, SCpb, SCna, SCnb, together with the respective freewheel diodesDCpa, DCpb, DCna, DCnb and respective temperature-sensitive diodes (notshown), form semiconductor modules 110Cpa, 110Cpb, 110Cna, 110Cnb,respectively.

A first end of the reactor 92 is electrically connected to a junctionbetween the upper-arm transformer switching elements SCpa, SCpb and thelower-arm voltage-transformation switching elements SCna, SCnb. A secondend of the reactor 92 is electrically connected to a positive terminalof a high-voltage battery 72. A negative terminal of the high-voltagebattery 72 is electrically connected to the emitters of the lower-armvoltage-transformation switching elements SCna, SCnb. An input capacitor91 is electrically connected to the high-voltage battery 72.

The first inverter 100 includes U-, V-, W-phase upper-arm switchingelements S1Up, S1Vp, S1Wp, and U-, V-, W-phase lower-arm switchingelements S1Un, S1Vn, S1Wn. The switching elements S1Up, S1Vp, S1Wp,S1Un, S1Vn, S1Wn are electrically connected in anti-parallel withrespective freewheel diodes D1Up, D1Vp, D1Wp, D1Un, D1Vn, D1Wn. As inthe first embodiment, the switching elements S1Up, S1Vp, S1Wp, S1Un,S1Vn, S1Wn, together with the respective freewheel diodes D1Up, D1Vp,D1Wp, D1Un, D1Vn, D1Wn and respective temperature-sensitive diodes (notshown), form semiconductor modules 120Up, 120Vp, 120Wp, 120Un, 120Vn,120Wn, respectively.

The second an inverter 102 includes U-, V-, W-phase upper-arm switchingelements S2Up, S2Vp, S2Wp, and U-, V-, W-phase lower-arm switchingelements S2Un, S2Vn, S2Wn. The switching elements S2Up, S2Vp, S2Wp,S2Un, S2Vn, S2Wn are electrically connected in anti-parallel withrespective freewheel diodes D2Up, D2Vp, D2Wp, D2Un, D2Vn, D2Wn. As inthe first embodiment, the switching elements S2Up, S2Vp, S2Wp, S2Un,S2Vn, S2Wn, together with the respective freewheel diodes D2Up, D2Vp,D2Wp, D2Un, D2Vn, D2Wn and respective temperature-sensitive diodes (notshown), form semiconductor modules 130Up, 130Vp, 130Wp, 130Un, 130Vn,130Wn, respectively.

Each of the first and second inverter 100, 102 has a similarconfiguration to that of the three-phase inverter 10 of the firstembodiment. Therefore, in the present embodiment, a detailed descriptionabout the first and second inverter 100, 102 will not be given here.

The first inverter 100 is electrically connected to the first motorgenerator 101. The first motor generator 101 acts as an alternator andas a starter for applying an initial torque to a crankshaft of a vehicleengine. The second inverter 102 is electrically connected to the secondmotor generator 103. Like the motor generator 70 of the firstembodiment, the second motor generator 103 acts as a prime mover or thelike.

The microcomputer 80 is configured to output operation signals to drivecircuits (not shown) of the respective switching elements S1Up, S1Vp,S1Wp, S1Un, S1Vn, S1Wn to drive the first motor generator 101 as analternator. This allows an alternating voltage input from the firstmotor generator 101 to the first inverter 100 to be converted into adirect voltage, which in turn is applied to the buck-boost converter 90.In the present embodiment, the operation signals are generated through aPWM process based on comparison of U-, V-, W-phase output voltagecommand values for the first inverter 100 with a carrier signal (e.g., atriangular waveform signal) in magnitude. The operation signals thusgenerated for the respective three phases of the first motor generator101 are, for example, signals for providing U-, V-, W-phase sinusoidalcurrents for the first motor generator 101 that are 120 degrees out ofphase in electric angle.

The microcomputer 80 is configured to output operation signals to drivecircuits (not shown) of the respective switching elements S2Up, S2Vp,S2Wp, S2Un, S2Vn, S2Wn to motoring-drive the second motor generator 103as an electrical motor or regeneration-drive the second motor generator103 as an alternator. In motoring drive, a direct voltage input from thebuck-boost converter 90 to the second inverter 102 is converted into analternating voltage, which in turn is applied to the second motorgenerator 103. In regeneration drive, an alternating voltage input fromthe second motor generator 103 to the second inverter 102 is convertedinto a direct voltage, which in turn is applied to the buck-boostconverter 90. In the present embodiment, the operation signals aregenerated through the PWM process.

The microcomputer 80 is configured to output operation signals to drivecircuits (not shown) of the respective voltage-transformation switchingelements SCpa, SCpb, SCna, SCnb to drive the buck-boost converter 90 asa boost converter or drive the buck-boost converter 90 as a buckconverter. More specifically, in voltage step-up operation tomotoring-drive the second motor generator 103, both the lower-armvoltage-transformation switching elements SCna, SCnb are turned on andoff in synchronization with each other with both the upper-armvoltage-transformation switching elements SCpa, SCpb kept in anoff-state. In voltage step-down operation to regeneration-drive thesecond motor generator 103, the upper-arm voltage-transformationswitching elements SCpa, SCpb are turned on and off in synchronizationwith each other with both the lower-arm voltage-transformation switchingelements SCna, SCnb kept in an off-state.

A frequency of the carrier signal (e.g., 5 kHz) used to generate theoperation signals for each of the inverters 100, 102 is set lower than afrequency of the carrier signal (e.g., 10 kHz) used to generate theoperation signals for the buck-boost converter 90.

A configuration for detecting temperatures of the respective switchingelements will now be explained with reference to FIG. 8. FIG. 8corresponds to FIG. 4 of the first embodiment. In FIG. 8, the circuitboard 20 is not shown.

As shown in FIG. 8, the drive circuits D2Up, D2Vp, D2Wp, D2Un, D2Vn,D2Wn configured to drive the respective switching elements S2Up, S2Vp,S2Wp, S2Un, S2Vn, S2Wn forming the second an inverter 102, photocouplersC2Up, C2Vp, C2Wp, C2Un, C2Vn, C2Wn, first and second multiplexers 140 a,140 b, and the microcomputer 80 are mounted on the circuit board. In thepresent embodiment, the first multiplexer 140 a has two input ports andone output port, and the second multiplexer 140 b has three input portsand one output port. The drive circuits D2Up, D2Vp, D2Wp, D2Un, D2Vn,D2Wn are configured to receive temperature signals fromtemperature-sensitive diodes T2Up, T2Vp, T2Wp, T2Un, T2Vn, T2Wn fordetecting temperatures of the respective switching elements S2Up, S2Vp,S2Wp, S2Un, S2Vn, S2Wn. The drive circuits D2Up, D2Vp, D2Wp, D2Un, D2Vn,D2Wn are configured to convert the received temperature signals intoduty signals, which in turn are input to the respective photocouplersC2Up, C2Vp, C2Wp, C2Un, C2Vn, C2Wn.

The drive circuits D1Up, D1Vp, D1Wp, D1Un, D1Vn, D1Wn are configured todrive the respective switching elements S1Up, S1Vp, S1Wp, S1Un, S1Vn,S1Wn forming the first inverter 100, photocouplers C1Up, C1Vp, C1Wp,C1Un, C1Vn, C1Wn, and third and fourth multiplexers 140 c, 140 d aremounted on the circuit board. In the present embodiment, each of thethird and fourth multiplexers 140 c, 140 d has three input ports and oneoutput port. The drive circuits D1Up, D1Vp, D1Wp, D1Un, D1Vn, D1Wn areconfigured to receive temperature signals from temperature-sensitivediodes T1Up, T1Vp, T1Wp, T1Un, T1Vn, T1Wn for detecting temperatures ofthe respective switching elements S1Up, S1Vp, S1Wp, S1Un, S1Vn, S1Wn.The drive circuits D1Up, D1Vp, D1Wp, D1Un, D1Vn, D1Wn are configured toconvert the received temperature signals into duty signals, which inturn are input to the respective photocouplers C1Up, C1Vp, C1Wp, C1Un,C1Vn, C1Wn.

The drive circuits DCpa, DCpb, DCna, DCnb are configured to drive therespective switching elements SCpa, SCpb, SCna, SCnb forming thebuck-boost converter 90, photocouplers CCpa, CCpb, CCna, CCnb, and fifthand sixth multiplexers 140 e, 140 f are mounted on the circuit board. Inthe present embodiment, each of the fifth and sixth multiplexers 140 e,140 f has two input ports and one output port. The drive circuits DCpa,DCpb, DCna, DCnb are configured to receive temperature signals fromtemperature-sensitive diodes TCpa, TCpb, TCna, TCnb for detectingtemperatures of the respective switching elements SCpa, SCpb, SCna,SCnb. The drive circuits DCpa, DCpb, DCna, DCnb are configured toconvert the received temperature signals into duty signals, which inturn are input to the respective photocouplers CCpa, CCpb, CCna, CCnb.

Temperature signals outputted from outputs of the respective U-, V-phaseupper-arm photocouplers C2Up, C2Vp are input to the respective inputports of the first multiplexer 140 a. The output port of the firstmultiplexer 140 a is electrically connected to a first input port T1 ofthe microcomputer 80 via a first electrical path L1. Outputs of therespective W-phase upper-arm photocoupler C2Wp and U-, V-phase lower-armphotocouplers C2Un, C2Vn are electrically connected to a second inputport T2 of the microcomputer 80 via the second multiplexer 140 b and asecond electrical path L2. An output of the W-phase lower-armphotocoupler C2Wn is electrically connected to a third input port T3 ofthe microcomputer 80 via a third electrical path L3.

Outputs of the respective U-, V-, W-phase upper-arm photocouplers C1Up,C1Vp, C1Wp are electrically connected to a fourth input port T4 of themicrocomputer 80 via a third multiplexer 140 c and a fourth electricalpath L4. Outputs of the respective U-, V-, W-phase lower-armphotocouplers C1Un, C1Vn, C1Wn are electrically connected to a fifthinput port T5 of the microcomputer 80 via a fourth multiplexer 140 d anda fifth electrical path L5.

Outputs of the respective upper-arm voltage-transformation photocouplersCCpa, CCpb are electrically connected to a sixth input port T6 of themicrocomputer 80 via a fifth multiplexer 140 e and a sixth electricalpath L6. Outputs of the respective lower-arm voltage-transformationphotocouplers CCna, CCnb are electrically connected to a seventh inputport T7 of the microcomputer 80 via a sixth multiplexer 140 f and aseventh electrical path L7.

The microcomputer 80 is configured to detect temperatures of therespective whole switching elements forming the first inverter 100, thesecond inverter 102, and the buck-boost converter 90 based on thetemperature signals received at the respective input port T1-T7 of themicrocomputer 80. The microcomputer 80 is configured to, whendetermining that the highest one ST of the detected temperatures exceedsa threshold temperature Tγ, conduct the power saving process.

In the present embodiment, a temperature signal from thetemperature-sensitive diode T2Wn associated with the W-phase lower-armswitching element S2Wn forming the second inverter 102 is input to themicrocomputer 80 without passing through any multiplexer. This isbecause, among the buck-boost converter 90, the first inverter 100, andthe second inverter 102, the switching elements forming the secondinverter 102 may be assumed to be hotter than the switching elementsforming the buck-boost converter 90 and the first inverter 100 duringuse. Particularly, in the present embodiment, among the switchingelements forming the second inverter 102, the W-phase lower-armswitching element S2Wn is assumed to be hottest during use.

The two-motor control system in a buck and boost configuration of thepresent embodiment can provide similar advantages to those of the firstembodiment.

Further, in the present embodiment, only the temperature signals of therespective switching elements forming the second inverter 102 are inputto the first and second multiplexers 140 a, 140 b. Only the temperaturesignals of the respective switching elements forming the first inverter100 are input to the third and fourth multiplexers 140 c, 140 d. Onlythe temperature signals of the respective switching elements forming thebuck-boost converter 90 are input to the fifth and sixth multiplexers140 e, 140 f. In such a configuration, the microcomputer 80 can readilydetermine each of the temperature signals received at the respectiveinput ports of the microcomputer 80 corresponds to which of thebuck-boost converter 90, the first inverter 100, and the second inverter102. For example, when a signal received at one of the input ports ofthe microcomputer 80 indicating the presence of an abnormality, themicrocomputer 80 can determine the signal has come from which of thebuck-boost converter 90, the first inverter 100, and the second inverter102.

Fourth Embodiment

There will now be explained a fourth embodiment of the presentinvention. Only differences of the fourth embodiment from the thirdembodiment will be explained with reference to the accompanyingdrawings. In the present embodiment, as shown in FIG. 9, for each of thebuck-boost converter 90, the first inverter 100, and the second inverter102, one temperature signal is input directly to the microcomputer 80without passing through any multiplexer. In FIG. 9, members same as themembers shown in FIG. 8 are assigned the same numbers.

As shown in FIG. 9, outputs of the respective U-, V-phase lower-armphotocouplers C1Un, C1Vn for the first inverter 100 are electricallyconnected to a fifth input port T5 of the microcomputer 80 via a fourthmultiplexer 140 g and a fifth electrical path L5. The output of theW-phase lower-arm photocoupler C1Wn is electrically connected directlyto a sixth input port T6 of the microcomputer 80 via a sixth electricalpath L6 without any multiplexer. This is because, in the presentembodiment, the W-phase lower-arm switching element S1Wn may be assumedto be hottest among the switching elements forming the first inverter100 during use.

Outputs of the respective voltage-transformation photocouplers CCpa,CCpb, CCna are electrically connected to a seventh input port T7 of themicrocomputer 80 via a fifth multiplexer 140 h and a seventh electricalpath L7. In addition, the output of the lower-arm voltage-transformationphotocoupler CCnb is are electrically connected to an eighth input portT8 of the microcomputer 80 via an eighth electrical path L8 without anymultiplexer. This is because, in the present embodiment, the lower-armvoltage-transformation switching element SCnb may be assumed to behottest among the switching elements forming the buck-boost converter 90during use.

Advantages of the present embodiment will now be explained. Theoperational aspect or the value of flowing current may be differentbetween the buck-boost converter 90, the first inverter 100, and thesecond inverter 102. Thus, heat generation amounts of the respectiveswitching elements may be different between the buck-boost converter 90,the first inverter 100, and the second inverter 102, which leads todifferent temperatures of the respective switching elements between thebuck-boost converter 90, the first inverter 100, and the second inverter102. In the present embodiment, for each of the buck-boost converter 90,the first inverter 100, and the second inverter 102, one temperaturesignal is input directly to the microcomputer 80 without passing throughany multiplexer. This can enhance the accuracy of detecting thetemperatures of the whole switching elements.

Fifth Embodiment

There will now be explained a fifth embodiment of the present invention.Only differences of the fifth embodiment from the fourth embodiment willbe explained with reference to the accompanying drawings. In the presentembodiment, as shown in FIG. 10, for the buck-boost converter 90, thetemperature signal of one of the upper-arm switching elements and thetemperature signal of one of the lower-arm switching elements are inputdirectly to the microcomputer 80 without passing through anymultiplexer. In FIG. 10, members same as the members shown in FIG. 9 areassigned the same numbers.

As shown in 10, the output of the upper-arm voltage-transformationphotocoupler CCpa is electrically connected to the seventh input port T7of the microcomputer 80 via the seventh electrical path L7 without anymultiplexer. This is because, in the present embodiment, the switchingelement SCpa may be assumed to be hottest among the upper-armvoltage-transformation switching elements SCpa, SCpb during use. Theoutputs of the respective voltage-transformation photocouplers CCpb,CCna are electrically connected to the eighth input port T8 of themicrocomputer 80 via a fifth multiplexer 140 i and the eighth electricalpath L8. The output of the lower-arm voltage-transformation photocouplerCCnb is electrically connected to a ninth input port T9 of themicrocomputer 80 via a ninth electrical path L9 without any multiplexer.This is because, in the present embodiment, the switching element SCpbmay be assumed to be hottest among the lower-arm voltage-transformationswitching elements SCna, SCnb during use.

Advantages of the present embodiment will now be explained. In thebuck-boost converter 90, the switching elements that are turned on andoff during the voltage step-up operation are different from theswitching elements that are turned on and off during the voltagestep-down operation. Therefore, during the voltage step-up operation,the temperatures of the respective lower-arm voltage-transformationswitching elements SCna, SCnb are higher than the temperatures of therespective upper-arm voltage-transformation switching elements SCpa,SCpb. During the voltage step-down operation, the temperatures of therespective upper-arm voltage-transformation switching elements SCpa,SCpb are higher than the temperatures of the respective lower-armvoltage-transformation a switching elements SCna, SCnb. Therefore, inthe present embodiment, the temperature signal of one of the upper-armswitching elements and the temperature signal of one of the lower-armswitching elements are input directly to the microcomputer 80 withoutpassing through any multiplexer. This can enhance the accuracy ofdetecting the temperatures of the whole switching elements.

Sixth Embodiment

There will now be explained a sixth embodiment of the present invention.Only differences of the sixth embodiment from the third to fifthembodiments will be explained with reference to the accompanyingdrawings. In the present embodiment, as shown in FIG. 11, the buck-boostconverter 90 a is modified in configuration. In FIG. 11, members same asthe members shown in FIG. 7 are assigned the same numbers.

In the present embodiment, as shown in FIG. 11, the buck-boost converter90 a includes a lower-arm series connection of first and secondswitching elements S1, S2 and an upper-arm series connection of thirdand fourth switching elements S3, S4. In the present embodiment, an IGBTis used for each of the switching elements S1, S2, S3, S4. The switchingelements S1, S2, S3, S4 are electrically connected in anti-parallel withrespective freewheel diodes D1, D2, D3, D4.

A junction between the second switching element S2 and the thirdswitching element S3 is electrically connected to the first end of thereactor 92. A junction between the first switching element S1 and thesecond switching element S2 is electrically connected to a junctionbetween the third switching element S3 and the fourth switching elementS4 through an auxiliary capacitor 94. The emitter of the first switchingelement S1 is the negative terminal of the high-voltage battery 72.

The voltage step-up operation and the voltage step-down operation of thebuck-boost converter 90 a will now be explained. In the presentembodiment, the voltage step-up operation is implemented by combinationsof first to fourth modes. In the first mode, the first and secondswitching elements S1, S2 are turned on, and the third and fourthswitching elements S3, S4 are turned off. In the second mode, the firstand third switching elements S1, S3 are turned on, and the second andfourth switching elements S2, S4 are turned off. In the third mode, thesecond and fourth switching elements S2, S4 are turned on, and the firstand third switching elements S1, S3 are turned off. In the fourth mode,the third and fourth switching elements S3, S4 are turned on, and thefirst and second switching elements S1, S2 are turned off. The voltagestep-up operation may be implemented by a cyclic sequence of modes, forexample, the first mode→the second mode→the first mode→the third mode orthe second mode→the fourth mode→the third mode→the fourth mode.

In the present embodiment, the voltage step-up operation is implementedby combinations of fifth to eighth modes. In the fifth mode, the firstto fourth switching elements S1-S4 are all turned off. In the sixthmode, the third switching element S3 is turned on, and the first, secondand fourth switching elements S1, S2, S4 are turned off. In the seventhmode, the fourth switching element S4 is turned on, and the first tothird switching elements S1-S3 are turned off. In the eighth mode, thethird and fourth switching elements S3, S4 are turned on, and the firstand second switching elements S1, S2 are turned off. The voltagestep-down operation may be implemented by a cyclic sequence of modes,for example, the fifth mode→the sixth mode→the fifth mode→the seventhmode or the eighth mode→the sixth mode→the eighth mode→the seventh mode.

As described above, as in the third to fifth embodiments, during thevoltage step-up operation, only the first and second lower-arm switchingelements S1, S2 are turned on and off. During the voltage step-downoperation, only the third and fourth upper-arm switching elements S3, S4are turned on and off. Therefore, as in the third to fifth embodimentsshown in FIGS. 8-10, a similar configuration for detecting temperaturesof the switching elements forming the buck-boost converter 90 a isapplicable in the present embodiment. More specifically, in the presentembodiment, for example, the lower-arm voltage-transformation switchingelements SCna, SCnb in each of the third to fifth embodiments may bereplaced with the first and second switching elements S1, S2, and theupper-arm voltage-ransformation switching elements SCpa, SCpb may bereplaced with the third and fourth switching elements S3, S4.

Seventh Embodiment

There will now be explained a seventh embodiment of the presentinvention. Only differences of the seventh embodiment from the thirdembodiment will be explained with reference to the accompanyingdrawings. In the present embodiment, as shown in FIG. 12, the buck-boostconverter 90 is absent in the motor control system. In FIG. 12, memberssame as the members shown in FIG. 7 are assigned the same numbers.

The present embodiment can thus provide similar advantages to those ofthe third embodiment.

Eighth Embodiment

There will now be explained an eighth embodiment of the presentinvention. Only differences of the eighth embodiment from the fifthembodiment will be explained with reference to the accompanyingdrawings. In the present embodiment, as in the buck-boost converter 90,each of the first inverter 100 and the second inverter 102 includesupper-arm parallel connections (for the respective phases) of twoswitching elements and lower-arm parallel connections (for therespective phases) of two switching elements. Accordingly, as shown inFIG. 13, in each of the first inverter 100 and the second inverter 102,each pair of two switching elements connected in parallel with eachother are turned on and off by their shared drive circuit. Each drivecircuit is configured to receive temperature signals from thetemperature-sensitive diodes respectively associated with the twoswitching elements connected in parallel with each other, and output atime-multiplexed signal for the received temperature signals to thephotocoupler. This is because the temperatures of the respective twoswitching elements connected in parallel with each other may bedifferent from each other. In FIG. 13, for each of the first inverter100 and the second inverter 102, each pair of semiconductor modulesincluding the respective two switching elements connected in parallelwith each other are assigned the same numbers.

As shown in FIG. 13, the temperature signals outputted from thetemperature-sensitive diodes TCpa, TCpb associated with the upper-armswitching elements are input to the shaped drive circuit DCpa. The drivecircuit DCpa is configured to output the time-multiplexed signal to theinput of the upper-arm voltage-transformation photocoupler CCpa. Theoutput of the upper-arm voltage-transformation photocoupler CCpa isconnected directly to a seventh input port T7 of the microcomputer 80via a seventh electrical path L7 without any multiplexer. Thetemperature signals outputted from the temperature-sensitive diodesTCna, TCnb associated with the lower-arm switching elements are input tothe shaped drive circuit DCna. The drive circuit DCna is configured tooutput the time-multiplexed signal to the input of the lower-armvoltage-transformation photocoupler CCna. The output of the lower-armvoltage-transformation photocoupler CCna is connected directly to aneighth input port T8 of the microcomputer 80 via an eighth electricalpath L8 without any multiplexer. In the present embodiment, the controlsystem does not include any multiplexer associated with the buck-boostconverter 90. The temperature detection configuration for each of thefirst inverter 100 and the second inverter 102 based on the timemultiplexing is similar to that of the buck-boost converter 90.

The time multiplexing performed by each drive circuit will now beexplained with reference to FIG. 14. In time multiplexing, the drivecircuit generates and outputs a frame signal including a header, a firsttemperature signal Ta, and a second temperature signal Tb, in thisorder. In the present embodiment, the temperature signals Ta, Tb areduty signals correlated to the temperatures. More specifically, as anexample, the upper-arm drive circuit DCpa of the buck-boost converter 90operates as follows. The first temperature signal Ta is a temperaturesignal of the switching element SCpa based on the output signal of thetemperature-sensitive diode TCpa, and the second temperature signal Tbis a temperature signal of the switching element SCpb based on theoutput signal of the temperature-sensitive diode TCpb. Upon receipt ofthe time-multiplexed frame signal, the microcomputer 80 calculatestemperatures of the respective two switching elements based on thereceived frame signal.

In the present embodiment, even though the upper-arm switching elementsare electrically connected in parallel with each other and the lower-armswitching elements are electrically connected in parallel with eachother, the temperature detection accuracy can be enhanced whilesupressing the number of components.

Other Embodiments

There will now be explained modifications to the respective aboveembodiments.

In the first embodiment, there are the plurality of multiplexers.Alternatively, the number of multiplexers may be one.

Power converters other than the three-phase inverter are applicable tothe present invention. Electronic devices having switching elements,other than power converters, may also be applicable. The number ofswitching elements in each of such power converters or electronicdevices is not limited to six, and may be equal to or greater thanthree, but not six. For each of such power converters or electronicdevices, at least three switching elements allow at least onetemperature signal to be input directly to the microcomputer without anymultiplexer and allows at least two temperature signals to be input tothe microcomputer via the multiplexer.

More specifically, such a system as above may include, for example, thetwo-motor control system having two motor generators. Since such asystem includes two three-phase inverters as power converters orelectronic devices, the number of switching elements is equal to orgreater than twelve, where the number of multiplexers is not limited totwo, and may be equal to or greater than three. For example, when thenumber of switching elements is twelve and the number of multiplexers isthree, first to three multiplexers may have three, four, and four inputports, respectively. Even though a difference in number of input portsbetween these multiplexers is up to one, variations in the lag time oftransfer of the temperature signal from the temperature-sensitive diodeto the microcomputer via the multiplexer can be minimized. This can thusminimize the time intervals between detection of temperatures of aspecific switching element.

In the first embodiment, only one temperature signal may be inputdirectly to the microcomputer without any multiplexer, where, as anexample, the first multiplexer may have three input ports.

Some specifications of the three-phase inverter 10 may cause the W-phaselower-arm semiconductor module 50Wn that is most far away from theupstream portion of the inlet line 30 a and adjacent the pressing member60 to be hottest during use.

In the first embodiment, for each of the multiplexers, when the numberof output ports is less than the number of input ports, the multiplexermay have two or more output ports.

Each switching element is not limited to the single IGBT, and may be aparallel connection of plural IGBTs. More specifically, collectorterminals of the plural IGBTs are electrically connected to each other,and emitter terminals of the plural IGBTs are electrically connected toeach other. In such a configuration, the actual temperature variation asshown in FIG. 5 will be increased due to a “parallel-connectionvariation” that is a variation in temperature during use between theplural IGBTs caused by a variation in flowing collector current betweenthe plural IGBTs. The parallel-connection variation exists in each ofthe detection element and the non-detection element shown in FIG. 5.Thus, the actual temperature variation may be doubled as compared withthe actual temperature variation of FIG. 5. Accordingly, the thresholdtemperature Ty needs to be set lower for safety. A temperature rangewhere use is restricted is thus prone to be enlarged. Therefore, in sucha configuration, it is more advantageous to detect temperatures of therespective whole switching elements.

The six switching elements are individually modularized as the sixsemiconductor modules. Alternatively, for example, the six switchingelements are connected in series with each other, and lower-armswitching elements may be modularized as a single semiconductor module.

Each insulating transfer element for transferring a signal from the highvoltage domain to the low voltage domain while electrically isolatingthe high and low voltage domains from each other is not limited to theoptical insulating transfer element. Alternatively, the insulatingtransfer element may be a magnetic insulating transfer element, such asa pulse transformer.

Instead of the IGBT, for example, a metal-oxide semiconductorfield-effect transistor (MOSFET) may be used as each of the switchingelements that produce heat when energized.

Each temperature signal output for outputting the temperature signalcorrelated to the temperature of one of the switching elements is notlimited to the temperature-sensitive diode. Alternatively, eachtemperature signal output for outputting the temperature signalcorrelated to the temperature of one of the switching elements may be athermistor. A copper pattern is formed on a first side (e.g., a topsurface) of an insulated substrate, and a heat sink is mounted on asecond side (e.g., a bottom surface) of the substrate. The switchingelement and the freewheel diode are mounted on the substrate bysoldering or the like, thereby forming a module. The switching elementand the freewheel diode are electrically connected via the pattern, andthe thermistor may be mounted on the pattern of the module. Heatproduced in the switching element or the freewheel diode dissipated tothe thermistor via the pattern. Therefore, the temperature of at leastone of the switching element and the freewheel diode can be detected.

Each power-conversion semiconductor element that produces heat whenenergized is not limited to the IGBT. Alternatively, eachpower-conversion semiconductor element that produces heat when energizedmay include a MOSFET or an RC-IGBT. The RC-IGBT is a diode-embedded IGBTsuch that the IGBT and the freewheel diode are mounted on the same chip.In addition, each power-conversion semiconductor element that producesheat when energized is not limited to the switching element as a powersemiconductor. Alternatively, the power-conversion semiconductorelements that produce heat when energized may include the freewheeldiode. For example, in the buck-boost converter, a large amount of heatmay be generated in the upper-arm freewheel diode during voltage step-upoperation. Therefore, it is advantageous to detect a temperature of thefreewheel diode.

In each of the third to sixth, and eighth embodiments, the buck-boostconverter is used. Alternatively, either a boost converter or a buckconverter may be used.

In the third embodiment, for example, one of the switching elementsforming the buck-boost converter 90 or the first inverter 100 may behottest among the whole switching elements forming the buck-boostconverter 90, the first inverter 100, and the second an inverter 102.For example, when one of the switching elements forming the buck-boostconverter 90 is hottest during use, only the switching elements formingthe buck-boost converter 90 may be connected directly to themicrocomputer 80 without any multiplexer.

In each of the third to seventh embodiments, for each of the buck-boostconverter 90, the first inverter 100, and the second inverter 102, atleast one multiplexer may have four or more input ports. For example,each of the buck-boost converter 90, the first inverter 100, and thesecond inverter 102 may each have a single multiplexer. In the thirdembodiment, for example, a single multiplexer for the second inverter102 may have five input ports, a single multiplexer for the firstinverter 100 may have six input ports, and a single multiplexer for thebuck-boost converter 90 may have four input ports.

In each of the third to seventh embodiments, the multiplexers may eachreceive temperature signals from at least two of the buck-boostconverter 90, the first inverter 100 and the second inverter 102. In theeighth embodiment, the multiplexers may each receive temperature signalsfrom both the first inverter 100 and the second inverter 102.

In each of the third to eighth embodiments, the number of motorgenerators may be greater than two.

In the third embodiment, the high-voltage battery 72 may be replacedwith a low-voltage battery having a lower output voltage (e.g., 12V)than the high-voltage battery 72. Such a configuration may be applied toa system where, for example, an engine is only one vehicle prime moverand the motor generator is used as an integrated starter generator (ISG)that integrates starter and alternator functionalities.

In the seventh embodiment, the high-voltage battery 72 electricallyconnected to the first inverter 100 may be replaced with a low-voltagebattery having a lower output voltage (e.g., 12V) than the high-voltagebattery 72. Such a configuration may be applied to a system where, forexample, an engine and a motor are mounted in the vehicle as vehicleprime movers and the first motor generator 101 is used as an integratedstarter generator (ISG) that integrates starter and alternatorfunctionalities.

In the eighth embodiment, the motor control system may not have thebuck-boost converter 90. In addition, in the eighth embodiment, themotor control system may include a single motor generator.

In each of the third to seventh embodiments, the buck-boost converter 90may be formed by parallel connections of three or more switchingelements, and each of the first and second inverters 100, 102 may beformed by parallel connections of two or more switching elements. In theeighth embodiment, each of the buck-boost converter 90, the firstinverter 100, and the second inverter 102 may be formed by parallelconnections of three or more switching elements, and each of the firstand second inverters 100, 102 may be formed by parallel connections ofthree or more switching elements. Further, at least one of the firstinverter 100, the second inverter 102, and the buck-boost converter 90may be formed by parallel connections of plural switching elements.

In the eighth embodiment, each drive circuit may not perform any timemultiplexing process. In such a case, each temperature-sensitive diodeindividually includes the drive circuit and the photocoupler.

In the eighth embodiment, the number of input ports for each of themultiplexers respectively corresponding to the first inverter 100 andthe second inverter 102 may be equal to or greater than four. Morespecifically, the number of input ports for the multiplexercorresponding to the second an inverter 102 may be five, and the numberof input ports for the multiplexer corresponding to the first aninverter 100 may be five. This allows the number of multiplexers foreach of the first inverter 100 and the second inverter 102 to be one.Given a multiplexer having ten input ports, the first inverter 100 andthe second inverter 102 may share such a multiplexer, which allows thenumber of multiplexers for the first inverter 100 and the secondinverter 102 to be one.

In each of the third to eighth embodiments, the outputs of therespective whole photocouplers electrically connected to the respectivedrive circuits may be connected directly to the input ports of themicrocomputer 80 without any multiplexer.

In each of the first and second embodiments, the inverter may be formedby parallel connections of plural switching elements, where for eachparallel connection of plural switching elements, the temperature forthe parallel connection of plural switching elements may be transferredfrom a drive circuit shared by the plural switching elements to themicrocomputer via the photocoupler by using the time multiplexingprocess.

What is claimed is:
 1. An apparatus for detecting temperatures ofpower-conversion semiconductor elements, the apparatus being applicableto a system including a plurality of power-conversion semiconductorelements that produce heat when energized, a plurality of temperaturesignal outputs associated with the respective power-conversionsemiconductor elements, the temperature signal outputs being configuredto output temperature signals correlated to temperatures of therespective power-conversion semiconductor elements, the apparatuscomprising: a microcomputer configured to detect the temperatures of therespective power-conversion semiconductor elements based on thetemperature signals outputted from the respective temperature signaloutputs, and at least one input-output interface having a plurality ofinput ports and an output port selectively connected to one of theplurality of input ports, wherein the temperature signal outputted fromat least one of the plurality of temperature signal outputs is inputdirectly to the microcomputer without passing through the at least oneinput-output interface, the temperature signals outputted from the othertwo or more temperature signal outputs are input to the respective inputports of the at least one input-output interface, the microcomputer isconfigured to detect the temperatures of the respective power-conversionsemiconductor elements based on the temperature signals received fromthe output port of the at least one input-output interface and thetemperature signal received directly from the at least one of theplurality of temperature signal outputs.
 2. The apparatus of claim 1,wherein the system comprising: an inverter configured to apply analternating voltage to a rotating electric machine, the inverterincluding plural pairs of upper-arm and lower-arm power-conversionsemiconductor elements, the plurality of temperature signal outputsassociated with the respective power-conversion semiconductor elementsforming the inverter being referred to as inverter outputs; and avoltage-transformation converter including plural pairs of upper-arm andlower-arm power-conversion semiconductor elements, thevoltage-transformation converter being configured to transmit power toand/or receive power from the inverter with voltage transformation, theplurality of temperature signal outputs associated with the respectivepower-conversion semiconductor elements forming thevoltage-transformation converter being referred to as converter outputs,wherein the temperature signal outputted from at least one of theplurality of the inverter outputs and the temperature signal outputtedfrom at least one of the plurality of the converter outputs are inputdirectly to the microcomputer without passing through the at least oneinput-output interface, and the temperature signals outputted from theother two or more inverter outputs and the temperature signals outputtedfrom the other two or more converter outputs are input to the respectiveinput ports of the at least one input-output interface.
 3. The apparatusof claim 2, wherein the power-conversion semiconductor elements formingthe inverter and the power-conversion semiconductor elements forming thevoltage-transformation converter include switching elements, one foreach power-conversion semiconductor element, the voltage-transformationconverter is a buck-boost converter configured to step up a voltagereceived from a direct-current (DC) power source to apply the stepped-upvoltage to the inverter during voltage step-up operation, and step downa direct voltage received from the inverter to apply the stepped-downvoltage to the DC power source during voltage step-down operation, thelower-arm switching elements of the voltage-transformation converter areturned on and off during the voltage step-up operation of thevoltage-transformation converter, and the upper-arm switching elementsof the voltage-transformation converter are turned on and off during thevoltage step-down operation of the voltage-transformation converter, thetemperature signal outputs associated with the respective upper-armpower-conversion semiconductor elements of the voltage-transformationconverter are referred to as upper-arm converter outputs, thetemperature signal outputs associated with the respective lower-armpower-conversion semiconductor elements of the voltage-transformationconverter are referred to as lower-arm converter outputs, and thetemperature signal outputted from at least one of the upper-armconverter outputs and the temperature signal outputted from at least oneof the lower-arm converter outputs are input directly to themicrocomputer without passing through the at least one input-outputinterface.
 4. The apparatus of claim 1, wherein the system comprising:at least one inverter configured to apply an alternating voltage to aleast one rotating electric machine, the at least one inverter includesplural pairs of upper-arm and lower-arm power-conversion semiconductorelements, the plurality of temperature signal outputs associated withthe respective power-conversion semiconductor elements forming theinverter being referred to as inverter outputs; and avoltage-transformation converter including plural pairs of upper-arm andlower-arm power-conversion semiconductor elements, thevoltage-transformation converter being configured to transmit power toand/or receive power from the at least one inverter with voltagetransformation, the plurality of temperature signal outputs associatedwith the respective power-conversion semiconductor elements forming thevoltage-transformation converter being referred to as converter outputs,wherein the least one rotating electric machine comprises a plurality ofrotating electric machines, the at least one inverter comprises aplurality of inverters, one for each rotating electric machine, each ofthe plurality of inverters being configured to apply the alternatingvoltage to a respective one of the plurality of rotating electricmachines, none of the temperature signals outputted from the respectiveconverter outputs are input to any one of the at least one input-outputinterface that receives at least one of the temperature signalsoutputted from the inverter outputs, and none of the temperature signalsoutputted from the respective inverter outputs are input to any one ofthe at least one input-output interface that receives at least one ofthe temperature signals outputted from the converter outputs.
 5. Theapparatus of claim 4, wherein the power-conversion semiconductorelements forming the inverter and the power-conversion semiconductorelements forming the voltage-transformation converter include switchingelements, one for each power-conversion semiconductor element, thevoltage-transformation converter is a buck-boost converter configured tostep up a voltage received from a direct-current (DC) power source toapply the stepped-up voltage to the inverter during voltage step-upoperation, and step down a direct voltage received from the inverter toapply the stepped-down voltage to the DC power source during voltagestep-down operation, the lower-arm switching elements of thevoltage-transformation converter are turned on and off during thevoltage step-up operation of the voltage-transformation converter, andthe upper-arm switching elements of the voltage-transformation converterare turned on and off during the voltage step-down operation of thevoltage-transformation converter, the temperature signal outputsassociated with the respective upper-arm power-conversion semiconductorelements of the voltage-transformation converter are referred to asupper-arm converter outputs, the temperature signal outputs associatedwith the respective lower-arm power-conversion semiconductor elements ofthe voltage-transformation converter are referred to as lower-armconverter outputs, none of the temperature signals outputted from therespective upper-arm converter outputs are input to any one of the atleast one input-output interface that receives at least one of thetemperature signals outputted from the lower-arm converter outputs andthe inverter outputs, and none of the temperature signals outputted fromthe respective lower-arm converter outputs are input to any one of theat least one input-output interface that receives at least one of thetemperature signals outputted from the upper-arm converter outputs andthe inverter outputs.
 6. The apparatus of claim 1, wherein the systemcomprising: an inverter configured to apply an alternating voltage to arotating electric machine, the inverter including plural pairs ofupper-arm and lower-arm power-conversion semiconductor elements, and avoltage-transformation converter including plural pairs of upper-arm andlower-arm power-conversion semiconductor elements, thevoltage-transformation converter being configured to transmit power toand/or receive power from the inverter with voltage transformation, atleast one of the power-conversion semiconductor elements forming atleast one of the inverter and the voltage-transformation converterincludes at least one parallel connection of switching elements, thevoltage-transformation converter is a buck-boost converter configured tostep up a voltage received from a direct-current (DC) power source toapply the stepped-up voltage to the inverter during voltage step-upoperation, and step down a direct voltage received from the inverter toapply the stepped-down voltage to the DC power source during voltagestep-down operation, the lower-arm switching elements of thevoltage-transformation converter are turned on and off during thevoltage step-up operation of the voltage-transformation converter, andthe upper-arm switching elements of the voltage-transformation converterare turned on and off during the voltage step-down operation of thevoltage-transformation converter, and the temperature signals outputtedfrom the temperature signal output associated with the at least oneparallel connection of switching elements are time-multiplexed and inputto the microcomputer.
 7. The apparatus of claim 6, wherein the pluralityof temperature signal outputs associated with the respectivepower-conversion semiconductor elements forming the inverter are groupedinto a plurality of parallel connections of power-conversionsemiconductor elements, the plurality of parallel connections ofpower-conversion semiconductor elements being referred to as groups ofinverter outputs, the plurality of temperature signal outputs associatedwith the respective upper-arm power-conversion semiconductor elements ofthe voltage-transformation converter are grouped into a plurality ofparallel connections of upper-arm power-conversion semiconductorelements, the plurality of parallel connections of upper-armpower-conversion semiconductor elements being referred to as groups ofupper-arm converter outputs, the plurality of temperature signal outputsassociated with the respective lower-arm power-conversion semiconductorelements of the voltage-transformation converter are grouped into aplurality of parallel connections of lower-arm power-conversionsemiconductor elements, the plurality of parallel connections oflower-arm power-conversion semiconductor elements being referred to asgroups of lower-arm converter outputs, the temperature signals outputtedfrom at least one of the plurality of groups of inverter outputs aretime-multiplexed and input directly to the microcomputer without passingthrough the at least one input-output interface, and the temperaturesignals outputted from the other two or more groups of inverter outputsare time-multiplexed and then input to the respective input ports of theat least one input-output interface, the temperature signals outputtedfrom the plurality of groups of upper-arm converter outputs aretime-multiplexed and input directly to the microcomputer without passingthrough the at least one input-output interface, and the temperaturesignals outputted from the plurality of groups of lower-arm converteroutputs are time-multiplexed and input directly to the microcomputerwithout passing through the at least one input-output interface.
 8. Theapparatus of claim 1, wherein the at least one of the plurality oftemperature signal outputs that outputs the temperature signal to beinput directly to the microcomputer without passing through the at leastone input-output interface is associated with the power-conversionsemiconductor element assumed to be hottest among the plurality ofpower-conversion semiconductor elements during use of the system.
 9. Theapparatus of claim 1, wherein the at least one input-output interfacecomprises a plurality of input-output interfaces, the output port ofeach of the plurality of input-output interfaces is connected tosequentially selected one of the plurality of input ports of theinput-output interface, the temperature signals outputted from the othertwo or more temperature signal outputs are input to the respective inputports of a respective one of the plurality of input-output interfaces,and the plurality of input-output interfaces are configured such that adifference in number of input ports between the plurality ofinput-output interfaces is equal to or less than one.
 10. The apparatusof claim 9, wherein a number of output ports of each of the plurality ofinput-output interfaces is one, and a number of input ports of each ofthe plurality of input-output interfaces is two.
 11. The apparatus ofclaim 1, wherein the plurality of power-conversion semiconductorelements comprise three or more series connections of upper-arm andlower-arm switching elements forming a three-phase inverter, and themicrocomputer has six or more input ports and are configured to detecttemperatures of the respective six or more switching elements formingthe three-phase inverter based on the temperature signals received atthe respective six or more input ports.
 12. The apparatus of claim 11,wherein at least one of the power-conversion semiconductor elementsincludes a parallel connection of switching elements, the temperaturesignals outputted from the temperature signal output associated with theparallel connection of switching elements are time-multiplexed and inputto the input port of the microcomputer, and the microcomputer has sixinput ports and are configured to detect temperatures of the respectiveswitching elements based on the temperature signals received at therespective six input ports.
 13. The apparatus of claim 1, wherein themicrocomputer is configured to, when determining that one of thetemperatures of the respective power-conversion semiconductor elementsexceeds a threshold temperature, de-energize the power-conversionsemiconductor elements or reduce power supplied to the power-conversionsemiconductor elements.
 14. An apparatus for detecting temperatures ofpower-conversion semiconductor elements, the apparatus being applicableto a system, the system including a plurality of power-conversionsemiconductor elements that produce heat when energized, and a pluralityof temperature signal outputs associated with the respectivepower-conversion semiconductor elements, the temperature signal outputsbeing configured to output temperature signals correlated totemperatures of the respective power-conversion semiconductor elements,the apparatus comprising a microcomputer having a plurality of inputports for receiving the temperature signals from the respectivetemperature signal outputs, each for a respective one of the temperaturesignals, and is configured to detect the temperatures of the respectivepower-conversion semiconductor elements based on the temperature signalsreceived at the respective input ports.